General/SubcatchmentDefinition/hydrology/en

Sub catchment Definition

For the rainfall-run off model the catchment area must be completely divided into sub catchments, which should reflect specific area characteristics. It is important to ensure that the sub catchment sizes do not vary too much. Each sub catchment is associated with a river strand, in which the run off from the area is drained. These watersheds define necessary boundaries of the sub catchments.

In order to delineate the sub catchment diverse data sources are required. The background information are the various causes that determine the flow path of the water in the area. Basically, the water flows along the strongest gradient. The data basis is therefore an elevation model. Optimally, contour lines are used, where further information remain directly visible. There are several options like automated definition of delineation lines on the basis of raster data (GRID) sub catchment, but other factors are not taken into account here except the elevation data. The selection of specific constraint points is important through which the boundaries are defined and this may be not possible by automated generation.

In the part of the sub catchment delineation, the data of the contour lines, sewers and retention basins are considered. KalypsoHydrology considers sewerage as that can drain sealed surfaces at specific points, and the retention of run off may be defined by channel networks by the modeller. Thus, run off from sealed and unsealed surfaces are parametrized differently. The basins are therefore aligned not only by the elevation data but also by the sewerage system.Retention basins are important, as mostly separate considerations are necessary for them. Firstly, they are considered as separate strands, so that the sub catchments should be divided according to whether they drain in the retention basin or behind. Furthermore, the arrangement of constraint points in front and behind the retention basin enables later on a better reflection of the simulated inflows and outflows in the model.

The Attribution is explained below : Digitization of network elements

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